This invention generally relates to a mechanism for taking a core drilling sample. In particular, the invention is directed to an improved method of taking core samples or unconsolidated samples from base rock or regolith at any depth using simple elements in a controlled, reliable fashion that does not subject the drill to external loads or movements and does require a stable or hard topographical surrounding to react loads, and more particularly, to a mechanism for breaking off the core sample once it has been drilled.
Prior art core sample methods consist of either drilling completely through the base rock in order to obtain a core sample or drilling to a desired depth and rocking the drill shaft back and forth until the core cracks away from the base rock. It is often impractical to drill completely through the rock to be sampled. The depth of the base rock may not be known or if it is known, it may be far deeper than the desired sampling depth. When obtaining a core sample by drilling to the desired depth and rocking the drill shaft back and forth, several problems arise. The cutting annulus must be great enough to provide sufficient movement of the drill shaft as it is rocked back and forth. If the drill depth is several times greater than the drill diameter, the cutting annulus must be further increased so as to provide the same rocking angle. Soon it becomes impractical to use this method of core extraction at any depth greater than several drill diameters. Drill shaft flexing will also detract from the available rocking angle. Even if these problems were surmountable, the relatively large external loads applied to the drill shaft must react to ground, which can be difficult in sandy or soft surroundings. Additionally, these sampling techniques cannot collect unconsolidated material, as it would simply fall out of the collection tube.
In accordance with the present invention, a core break-off mechanism comprises: an inner, core break-off tube extending along a tube axis which is sleeved within and angularly rotatable relative to an outer drill tube, wherein the core break-off tube has a tubular wall of varying thickness such that its inside diameter (C-ID) is offset with respect to its outside diameter (C-OD) by a predetermined amount in a radial direction transverse to the tube axis, and the drill tube has a tubular wall of varying thickness such that its inside diameter (D-ID) is offset with respect to its outside diameter (D-OD) by the same pre-determined amount in a radial direction, and wherein the drill tube has a drill end and a stepped indented shoulder on one lateral side of the tube axis proximate said drill end by which an end of the core break-off tube is retained within the drill tube, whereby when the break-off tube and the drill tube are held in one relative rotational alignment, the two offsets cancel each other such that the D-OD of the drill tube and the C-ID of the break-off tube are centered together on the tube axis and are in positional alignment for drilling a core from base rock to a desired depth, and when the break-off tube is rotated 180 degrees with respect to the drill tube, the offsets add together, causing the rock core within the inner tube to become radially displaced by a distance equal to the sum of the two offsets so as to generate sufficient force to break off the rock core from the base rock.
The invention the method of core break-off using offset tubes. It also includes other features to improve the operation of the drill assembly. Through shape modification, the tubes can be used to fully enclose samples, thus ensuring capture of rock or unconsolidated samples. A pushrod can be used for core extraction, as well as aid in drill stability, and provide an extension to the core drill bit. A combination of bit locking balls and grooves provide automated drill bit change-out capability. The drill assembly provides the ability to capture rock or unconsolidated samples without imparting reaction loads to the local terrain.
Other objects, features, and advantages of the present invention will be explained in the following detailed description of the invention having reference to the appended drawings.